The present invention relates to a device for measuring pupil diameter.
In a variety of ophthalmic diagnostic procedures, it is desirable to measure the diameter of the patient's pupil. The size of the human pupil is governed by the antagonistic actions of the dilator and sphincter muscles in the iris that are controlled by sympathetic and parasympathetic nerves, respectively. Several factors are known to affect pupil size, including retinal illuminance, the accommodative state of the lens and a variety of sensory and emotional conditions. The size of the pupil also tends to change with age, with elderly patients having relatively smaller pupils as a group. Size may also be influenced by certain diseases and conditions of ill health or pharmacological effects.
One problem associated with measuring pupil size is that the pupil is never entirely at rest but undergoes small, continuous oscillations known as hippus. As a result, to measure the pupil accurately requires measuring the pupil over a short period of time to determine an average pupil diameter. The measurement process is made more difficult by the natural body movements of the patient and the examiner. Other problems in achieving consistent pupil measurements in the same environment are control of illumination in the examining room. Light meters are often used to identify the amount of light available so as to assure similarity of conditions at different patient visits.
Prior art pupil measuring devices have included simple rulers graduated in millimeters and rulers having millimeter graduations on one side and circular or semicircular marks of fixed diameter on the other side. One such ruler is commonly referred to as the "Rosenbaum" ruler because it was designed by J. G. Rosenbaum, M.D. While these rulers were the most commonly used pupil measuring devices prior to the present invention, they had several disadvantages. For example, these rulers generally are printed on opaque cardstock, making it difficult to line up the graduations with the patient's eye. Patients also are more likely to move or become uncomfortable when a solid object is placed over the eye, creating a potential safety issue because of the hard, non-flexible material and sharp edges used in prior art pupillometers. In addition, prior art pupillometers contain only one set of either graduations or marks, requiring that the pupillometer be moved to measure alternate eyes. Such movement increases examination time and patient discomfort and that can be used quickly.
Accordingly, a need continues to exist for an accurate pupillometer that minimizes patient discomfort.